The enzyme, described from the mitochondria of plants and some fungi and protists, is an alternative terminal oxidase that is not sensitive to cyanide inhibition and does not generate a proton motive force. Unlike the electrogenic terminal oxidases that contain hemes (cf. EC 1.10.3.10 and EC 1.10.3.14), this enzyme contains a dinuclear non-heme iron complex. The function of this oxidase is believed to be dissipating excess reducing power, minimizing oxidative stress, and optimizing photosynthesis in response to changing conditions.